The first and last testament of Ned Kelly, Australia's iconic criminal, was recently handed over to the State Library of Victoria and posted on the internet. The Jerilderie letter's belated placement in the public domain has reignited a passionate debate in Australia about the elusive bushranger and why he means so much to the country.

A priceless, scribbled polemic, it is practically the only surviving fragment of evidence of the short life of Kelly, who was hanged in 1880. Souvenir hunters have decimated the remains of some of Kelly's childhood homes. His haunts, such as Stringybark Creek, where his gang shot dead three policemen, go unmarked. Even Kelly's skull is missing - stolen from Old Melbourne Gaol in 1978

"I wish to acquaint you with some of the occurrences of the present, past and future," is Kelly's opening line. What follows is a passionate, hand-written 8,300-word rage against the authorities' treatment of him and other, similarly impoverished, Irish-Australians, struggling to escape their convict histories and survive in the country's hot, harsh environment.

Kelly dictated the Jerilderie letter to his friend Joe Byrne, when they, along with Ned's younger brother Dan and Steve Hart, were holding up the entire town of Jerilderie in 1879. With rumours of the exploits of the "Kelly Gang" rife in Victoria, Ned displayed an early grasp of the need for good PR, giving the letter to an accountant with the order that it be printed and published. But the authorities stepped in, denied Kelly publicity, and the incendiary letter never saw the light of day.

Kelly only had a few more months on the run before he was captured and killed. The letter went missing for 90 years, while the Kelly legend slowly grew.

Kelly was not simply famous for outwitting the police and committing several audacious robberies, before being captured after a dramatic shoot-out during which he protected himself in a striking, hand-forged metal helmet and body-armour.

Word also spread of his generosity, after he gave money he robbed to impoverished settlers. He was famed for his good manners as well, at a time when the Australian authorities - the judges and the police - were corrupt and oppressive, particularly in their treatment of the Irish Catholics descended from convicts, of which Kelly and his large, unruly family, were an example.

For some contemporary commentators, the Jerilderie letter is aggressive self-aggrandisement; for others it is a proto-republican document, almost a Communist Manifesto for the poor settlers of Australia.

"It contains the available fragments of a rebel manifesto that underlay his attempt to proclaim a republic in the north-east [of the Australian state of Victoria]," Kelly scholar Ian Jones says. The letter's survival owes much to Jones, who was tipped off about its existence in 1969 and watched over it as it passed through a series of private owners. "It presents the Kelly voice - passionate, vivid, sometimes poetic, often funny," Jones adds.

The letter inspired Peter Carey's novel, The True History of the Kelly Gang. Published in Britain in January, the ironically named "True History" has been a bestseller in Australia this autumn. Carey writes in the stream-of-consciousness style of the Jerilderie letter, imagining Ned's emotional life - a mystery to this day.

"When I was about 20 I first read the Jerilderie letter and loved it so much that I sat down and typed it all up and carried it with me for years and years," says Carey. "He's very passionate, he's very Irish, he's very funny. It's filled with rage and vindictiveness." For instance, Kelly describes the police as "big, ugly, fat-necked, wombat-headed, big-bellied, magpie-legged, narrow-hipped, splay-footed sons of Irish bailiffs or English landlords".

Kelly's passion is reciprocated. Today, opinions of him remain fiercely polarised. For some, he was a latter-day saint, fighting the tyranny of Australia's upper class, the English settlers. For others, the continuing veneration of Kelly and Australia's convict classes is an indictment of a nation short of real heroes. One commentator in The Australian newspaper recently predicted that had Kelly not been hanged at 25, he "would have become the Pol Pot of north-east Victoria".

But Kelly historian Jones is fighting against such extreme views. "To dismiss Kelly as a horse thief and cop killer is on a par with seeing Jesus as an executed rebel who doesn't seem to have got on terribly well with his mum," he says.

"He was of convict stock and he proved himself to be more decent than the police," says Carey. "I think his wit, his decency and his courage showed that we were not to be the victims of our past, that we could, given the right circumstances, be an amazing people and I think that's why we continue to value him."